Scattering occurs when light irradiates a substance. During scattering, the wavelengths of most of the scattered light do not change, and the scattering radiation without any wavelength change is called Rayleigh scattering; but the wavelengths of a small part of the scattered light will increase or decrease, and the scattering radiation with wavelength change is called Raman scattering, whose corresponding spectrum is called Raman spectrum. The Raman spectrum is a vibration spectrum of molecules. By detecting the Raman spectrum of a substance, it is possible to know what the detected substance is or which component it contains, so the Raman spectrum can be used as the “fingerprint” for identification of substances. In view of this, the Raman spectrum has important application in such fields as medicine, food security, cultural relic and jewel authentication, and security check, etc. Meanwhile, with the more and more wide application of the Raman spectrum in these fields, there is a need for a Raman spectrometer capable of fast on-site detection to be adapted for different environments of various occasions of application. However, the characteristics of the laser light for exciting the Raman scattering of the substance, such as frequency and power, etc., will change with the environment temperature and the time of use, thus the detected Raman spectrum will also change. In addition, with respect to a Raman spectrometer that is frequently moved, the light path structure or the like of the system may be changed because of shaking, etc. during transportation and using, resulting in changes in the excitation efficiency and the signal collection efficiency for the excited Raman light, thus the Raman spectrum might change when the system detects the same sample at different time and in different environment. Raman spectrometers for scientific research mostly use a laser having stable frequency and power as the excitation light source, and have strict requirement on the operating environment. However, a laser having stable frequency and power is expensive, which hinders the popularization of the Raman spectrometer. Even if the laser with stable frequency and power is used, the power thereof will attenuate after using for some time, which will result in uncertain results of detection.